International Geophysical Year (IGY), worldwide program of geophysical research that was conducted from July 1957 to December 1958. IGY was directed toward a systematic study of the Earth and its planetary environment. The IGY encompassed research in 11 fields of geophysics: aurora and airglow, cosmic rays, geomagnetism, glaciology, gravity, ionospheric physics, longitude and latitude determinations, meteorology, oceanography, seismology, and solar activity. Because the IGY period was chosen to coincide with the maximum sunspot cycle, when solar flares and other disturbances are prevalent, research on the Sun was especially significant.

In 1950 a group of geophysicists led by the American scientist Lloyd V. Berkner proposed a third International Polar Year, an international scientific effort that would utilize the advances made in instrumentation, rocketry, and information processing since the Second International Polar Year of 1932–33. These proposals soon broadened from the field of polar studies to a wider array of geophysical research. The parent body of international scientific organizations—the International Council of Scientific Unions—sanctioned the broader study of proposals for what became known as the International Geophysical Year. National IGY committees were then established by scientific organizations in many countries, and more than 70 nations ended up cooperating in IGY.

The IGY pioneered in the use of rocketry to conduct studies of high-altitude and upper-atmosphere phenomena. Several of the earliest artificial satellites launched by the Soviet Union and the United States in the late 1950s were used to gather data for the IGY.

In retrospect, perhaps the most important achievement of the IGY was its verification in 1958 of scientists’ suggestion that there existed a continuous system of submarine mid-oceanic ridges that encircled the globe. The implications of this mountain chain, the largest on Earth, were only understood in the 1970s with the recognition of plate tectonics as a basic phenomenon of the Earth’s crust.

The discovery of the Van Allen radiation belts, which surround the Earth at altitudes of hundreds and thousands of kilometres, was another major achievement of IGY. The inner Van Allen belt was first delineated by instruments aboard the early Explorer satellites in 1958, and the space probes Pioneers III and IV discovered the second Van Allen belt soon afterward. Specific discoveries and findings represented only a part of the technical results of IGY. Most of the effort involved the collection of synoptic data—i.e., data that gave a comprehensive overview of global physical phenomena.

The success of the IGY inspired the formation of several other cooperative international research programs, notably the International Years of the Quiet Sun (1964–65), the International Hydrological Decade (1965–75), and the International Decade of Ocean Exploration (1970–80).

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